1. Field of the Invention
The present invention relates generally to metal working machinery and, more particularly, to a gage and method for determining the true dead center of a workpiece and spindle center line on a lathe or milling machine.
2. Description of the Related Art
Human beings have constantly sought better ways to work metal into objects ever since man discovered that certain rocks when heated oozed a substance that when cooled became very hard and was capable of being of formed. Liquid metal was poured into molds of desired shape and then allowed to cool. The metal object was then further formed by grinding the edges to form a cutting surface or the object was bent to a desired shape. In this fashion, spears, knives, tools and utensils were fashioned. Metal working through the iron age, copper age, and bronze age remained pretty much the same. This continued through the late 1800""s when the local blacksmith who forged and repaired metal items was one of the most important persons in the community.
The industrial revolution brought about dramatic changes in the metal working industry with the introduction of the blast furnace where large amounts of metal, typically iron and steel, could be extracted from ore. With large amounts of steel and iron now available virtually anything could now be manufactured from metal. This also required that the methods by which metal was formed into goods had to be improved in terms of not only speed but quality as well. Machinery powered by the electric motor were developed that could cut pieces of steel stock into desirable shapes. Machines were also developed that could selectively cut portions of a piece of metal stock by rotating the stock and pressing a special tool against the stock. The tool had a sharp edge which would cut a small portion of metal off the surface of the metal stock. The tool could then be pushed further into the stock or moved along the length of the stock. In this fashion bars of steel or other metal could be shaped into various pieces for making parts for all types of equipment and goods. This was the beginning of the metal working lathe as it is known today. Other machines were also developed which could selectively cut a piece of metal stock. The milling machine can cut a desired shape into a piece of metal stock by moving the stock into a rotating tool which has a sharpened edge. A series of adjustable hand wheels allows the machine operator to controllably guide the workpiece into the rotating tool. For decades the milling machine and lathe were the mainstay of the metal working industry which was the foundation of industry worldwide.
With the invention of computers, computer logic was added to guide the sequence in which the tool engaged the workpiece in both lathes and milling machines. In fact, machines were developed which performed both the function of a milling machine and lathe by utilizing a retractable turret which could rotate the appropriate tool to the workpiece upon the appropriate computer command. These machines are known as Computer Numerically Controlled (CNC) machines. In this fashion, a rotating milling machine tool could engage a workpiece followed by any one from a number of other cutting tools arranged radially on the rotating turret, each presumably positioned on the workpiece centerline. It is common to have several different tools for forming the workpiece in the lathe configuration.
In either case, whether it be an old variety lathe employing a single metal working tool or a CNC machine having numerous metal working tools, it is very important the tool be properly positioned relative to the workpiece. An incorrectly positioned tool can improperly cut a workpiece, xe2x80x9cscuffingxe2x80x9d the surface, causing tool life robbing chatter, or total catastrophic failure. The most desirable position for the tool is to have the tool""s cutting point directly in the same plane or slightly ahead of the plane of the workpiece""s centerline. A tool slightly ahead of the plane of the workpiece""s centerline will experience a compression as the workpiece rotates into the tool. A tool slightly behind the plane of a workpiece centerline will experience a shearing force which is very destructive to ultra-hard metal cutting edges. It is well known in the field of material science that a material can withstand much larger compressive forces than shear forces. Therefore, it is imperative to ensure the proper alignment of the tool with the plane of the workpiece""s centerline. The present invention fulfills this need by providing a device and method to determine the exact position of a tool holder pocket relative to the machine tool spindle and workpiece centerline. The xe2x80x9cDead Centerxe2x80x9d device determines how much to adjust and align the tool properly.
In the related art, there exists many patents for lathes and milling machines employing CNC technology to direct and control tool engagement with the workpiece. Many of these patents employ logic to ensure the placement of the tool in the correct position on the workpiece. However, these devices are quite technically complex and are integrally designed into the machine. They require elaborate sensors, servos, and controllers in addition to the software necessary to control these devices. These type of devices are of no use to existing conventional lathes or milling machines. Nor are they of any use to existing CNC machines that do not have an integral pre-existing tool alignment system. The art is completely devoid of an inexpensive aftermarket device for determining the true centerline of a workpiece on lathes and milling machines which do not have built in centering capabilities. A need has therefore been felt for an improved but less complex mechanism and method for determining the true centerline of a workpiece on lathes and milling machines. The present invention fulfills this need.
A search of the prior art did not disclose any patents that read directly on the claims of the instant invention; however, the following references were considered related:
It is therefore an object of the present invention to provide an aftermarket gage and method for determining the true centerline of a workpiece on a conventional CNC lathe or milling machine.
It is another object of the present invention to provide a gage and method to measure the distance that a machine cutting tool or tool holder pocket is offset from the true centerline of a workpiece on a conventional or CNC lathe or milling machine.
It is yet another object of the present invention to provide a simple and inexpensive gage and method to measure the distance that a machine cutting tool or tool holder pocket is offset from the true centerline of a workpiece on a conventional or CNC lathe or milling machine.
It is still yet another object of the present invention to use a set of conventional feeler gauges to measure the gap between the bottom edge of the gage and the workpiece to determine the distance that a machine cutting tool or tool holder pocket is offset from the true centerline of a workpiece on a conventional or CNC lathe or milling machine.
It is yet still another object of the present invention to provide a generous assortment of metal shims available as industry standard thicknesses to match various sizes on a conventional feeler gage.
It is another object of the present invention to use a metal shim with the same thickness as the gap between the bottom of the gage and the workpiece as measured by the feeler gage to offset the tool in the tool holder so that it is aligned perfectly with the centerline of the workpiece.
It is yet another object of the present invention to use magnets on the side of the gage to temporarily hold the gage in the tool holder pocket while the gap between the bottom of the gage and the workpiece is measured with the feeler gage.
Briefly described according to one embodiment of the present invention, a gage and method for determining the true centerline of a workpiece or tool holder pocket on a conventional or CNC lathe or milling machine is provided consisting of a one piece gage cut from a suitable material such as high speed steel, tool steel, or stainless steel. The gage is essentially a flat metal bar with an arm on one end with a width corresponding to the dimensions of a tool holder on a conventional or CNC lathe or milling machine. The other end is Y-shaped having an upperwardly protruding arm with a upwardly sloping front edge located on the upper edge of the bar and a downwardly sloping front edge. Key to the functionality of the gage is the angle between the upperwardly sloping front edge on the uppwardly protruding arm and the downwardly sloping front edge of the bar. By placing the upperwardly sloping front edge of the uppwardly protruding arm firmly against a workpiece mounted in a conventional or CNC lathe or milling machine one can determine the variance between the machine tool holder pocket and the machine tool spindle. The gap present between the downwardly sloping front edge of the gage and the workpiece is the exact measurement of that variance, either plus or minus. Because of the geometry of the angles between the downwardly sloping front edge of the gage, the upwardly sloping edge of the upwardly protruding arm, and the workpiece, this gap is exactly equal to the distance the two centerlines or planes of reference are out of alignment. This gap can be measured by a conventional feeler gage. The tool holder pocket or tool holder, can be adjusted that distance to match the two planes of reference. Magnets fixed on the sides of the gage temporarily hold it while the variance is measured.